1) Field of the Invention
The present invention relates generally to commercial walk-behind mowers or similar vehicles with a transmission and PTO and, more specifically, to an interlock circuit for such vehicles.
2) Related Art
Currently available vehicles with key, transmission and PTO switches, such as wide area walk-behind mowers, have a transmission that automatically locks into neutral when the operator releases a bail located on the implement handle. Except during vehicle starting, the automatic locking into neutral feature eliminated need for a circuit that tied into the transmission neutral switch. There is a need to tie into the neutral switch, however, on models of similar vehicles that have a transmission clutch which is engaged while the bail is released to prevent vehicle movement when an operator is not present to hold the bail. In order to meet preselected requirements, such as no engine starting unless the PTO switch is off, the transmission is in neutral, and the key switch is on, a different interlock circuit is required than is available on vehicles with an automatic locking into neutral feature.
Some of the interlock circuits for walk-behind vehicles use commercially available electronic modules connected to switch structure on the vehicle. However, maintaining reliable module terminal connections is a continuing problem in the hostile operating environment, and terminal corrosion reduces the reliability of the circuits. Providing an interlock circuit that is simple, relatively inexpensive, and reliable and which uses components similar to those used in previous circuits to keep the number of parts to a minimum has been a problem. Providing an interlock circuit that can be used with pull start or electric start engines, or with engines where an electric start is added to the pull start so either can be used for starting, has also been a problem. Such a circuit must also permit continued running of the engine when the PTO and transmission are engaged when operator presence is indicated at a specific area on the vehicle.